1. Field of the Invention
The invention relates to a valve for use in a fluid pump for elevating fluids, and in particular, to a valve for use in a fluid pump for raising petroleum fluids through production tubing in completed oil and gas wells.
2. Description of Related Art
A conventional oil well includes a cased well bore with one or more strings of tubing extending downwardly through the casing into the oil, or other petroleum fluid, contained in the sub-surface mineral formation to be produced. The casing is perforated at the level of the production zone to permit fluid flow from the formation into the casing, and the lower end of the tubing string is generally open to provide entry for the fluid into the tubing.
One type of pump conventionally employed in structures of the type described is wedged into an internal constriction, or seating nipple, formed internally of the tubing below the fluid level. A metallic enlargement on the external body of the pump prevents it from traveling below the seating nipple and resilient seal rings on the body of the pump housing, or pump barrel, act to form a leak proof seal between the seating nipple and the pump housing, or barrel. The pump is generally driven by a mechanical linkage of metal or fiberglass rods, generally referred to as sucker rods, or valve rods, which extend from the pump to the well surface. The valve rod, or sucker rod, linkage is powered in a reciprocating motion by a conventional mechanical apparatus usually called a pumping unit located at the well surface.
The conventional pump itself generally includes a housing through which a piston or plunger is reciprocated by the sucker rod, or valve rod, linkage. In its simplest form, the conventional pump of the type described often includes a number of conventional ball and seat valves with at least one such valve in, or above, the piston, often referred to as the traveling valve assembly, and at least one other valve at the inlet port of the housing or barrel, often referred to as the standing valve assembly. On the upstroke of the plunger, the ball in the standing valve assembly is drawn away from its seat and the ball of the traveling valve assembly is forced over its seat to draw fluid from below the seating nipple and into the housing. On the piston's downstroke, the ball in the standing valve assembly is forced onto its seat and the ball in the traveling valve assembly moves away from its seat to allow the piston to move downwardly through the fluid contained in the housing. On the subsequent upstroke, the closing of the traveling valve assembly forces the fluid above the piston out of the housing through the outlet ports and into the tubing above the seating nipple and simultaneously fills the housing below the piston with fluid. Repetition of this cycle eventually fills the tubing string and causes the fluid to flow to the surface.
The previously described pump, or some variation thereof, is probably the most widely employed in applications where it is desired to drive a sub-surface pump by a surface powered, mechanical linkage. A significant problem in pumps of this type is generally known as a "pumped-off well" as will be hereinafter described with reference to one standing valve and one traveling valve; however, it should be understood that similar effects occur when more than one valve is used. Either initially, or eventually, the fluid in the reservoir is at a low pressure. On the upstroke of the plunger, the ball in the standing valve is initially drawn away from its seat, and the ball of the traveling valve is forced over its seat to draw fluid from below the seating nipple and into the housing. However, before a substantial portion of the upstroke is completed, the pressure of the fluid in the reservoir acting upon the ball in the standing valve is substantially reduced to the extent that the ball in the standing valve fails to be drawn away from its seat. Therefore, the ball in the standing valve blocks the passageway into the housing and prevents fluid from being drawn into the housing during the remaining portion of the upstroke. Similar problems occur on the downstroke with the ball in the traveling valve. Therefore, this "pumped-off well" condition results in substantially less fluid being brought to the surface during every stroke of the pump. This condition generally continues and tends to become more of a problem as the pressure of the fluid reservoir decreases.
Additionally, a significant problem is found in all other wells that incorporate the mechanical pumping device described above. Generally, in these other wells the seat and ball of the valves described above create a restriction and increase the frictional drag on the flow of reservoir fluids into the pump.
Accordingly, prior to the development of the present invention, there has not been a valve for use in a fluid pump for raising petroleum fluids through production tubing in a completed oil well which: increases the amount of fluid entering the housing, or barrel, for each stroke of the pump; increases the amount of time a ball is drawn and held away from its seat, thereby reducing the undesirable effects of a "pumped-off well" and reducing the frictional drag on the flow of reservoir fluids into the pump in all other wells; and is economical to use without frequent replacement of components. Therefore, the art has sought a valve for use in a sucker rod actuated fluid pump for raising petroleum fluids through production tubing in completed oil wells which: increases the amount of fluid entering the housing; increases the amount of time a ball is drawn and held away from its seat, thereby reducing the undesirable effects of a "pumped-off well" and reducing the frictional drag on the flow of reservoir fluids into the pump in other types of wells; and is more economical to use.